[Investigation of the relation between pigment composition and CO2 exchange in the blue-green alga anacystis nidulans].

Changes in culture conditions caused strong changes in the pigment composition in the blue-green alga Anacystis nidulans. Under "normal" illumination (white light; 0.6·10(3) erg/cm(2)·sec) the relation between the amounts of chlorophyll a and phycocyanin was 1:6.6. In a high light intensity (20.8·10(3) erg/cm(2)·sec) the phycocyanin content was reduced and the relations thus changed to 1:1.9. Growing the algae in red light of high intensity (20·10(3) erg/cm(2)·sec) increased the phycocyanin content; the chlorophyll a: phycocyanin relation was then 1:12.1.The action spectrum of apparent photosynthesis showed a minimum at 473 nm in all three cultures. The maximum of photosynthesis in low light cultures fell in the absorption region of phycocyanin at 621 nm. The action spectrum of the red light culture showed a reduced rate of photosynthesis in the same region. The strong light culture had an action spectrum similar to that of the red light culture with a maximum at 651 nm. The differing action spectrum of the low light culture may be a result of interruption in the energy transfer from phycocyanin to chlorophyll a within pigment system II.The transients of CO2 exchange are independent of the pigment composition. Two different types of transients were found depending on the wavelength of the incident light. In red light of 550-650 nm a higher stationary rate was reached after a maximum of photosynthesis at the beginning of the illumination period. In blue and far red light a lower rate was found after the first maximum. Following a illumination period in blue or far red light a CO2 evolution in the dark was observed. On the other hand, this CO2 evolution was not found after illumination with red light. These effects are possiblt caused by a decarboxylation reaction (photorespiration) which occurs only in blue and far red light.